@Entity
@Table(name = "purchase_order")
public class PurchaseOrder {
    @Id
    private String orderNumber;

    @ManyToOne
    @JoinColumn(name = "supplier_id", nullable = false)
    private Supplier supplier;

    private LocalDate orderDate;
    private LocalDate expectedDeliveryDate;
    private LocalDate actualDeliveryDate;

    // 其他订单字段...
}